IS & Ex

Alarm system upgrade from Omniflex

September 2019 IS & Ex

Fiddler’s Ferry Power Station was constructed by the CEGB (Central Electricity Generating Board) in the UK and came into full operation in 1973. It has four 500 MW sets, giving a total generating capacity of 2 GW, and is fuelled by coal. When the facility needed to replace an obsolete alarm system, management chose a solution from Omniflex.

The challenge

The existing alarm system consisted of Bristol Babcock logic racks, which fed data via Modbus serial, into the APMS (advanced plant management system). The new alarm system was required to replicate this functionality, but using Modbus TCP, via dual redundant Ethernet networks. Furthermore, some remote panels located around the plant, required incorporation into the new system. With space limitation in some of the existing panels, the replacement nodes had to be engineered to fit in the available spaces and ease of installation needed to be taken into account.

Their APMS was not compatible with the Sequence of Events timestamps, therefore an engineering scada workstation had to be provided to log and display the alarms.

To provide the required functionality the following components were required:

• Omniflex A3e Maxilarm modular alarm logic nodes.

• Omniflex Sequence of Events modules to timestamp alarms (at source).

• Ability to interface with the existing APMS via Modbus TCP.

• Time synchronisation of all nodes using a GPS Time Sync Module.

• Engineering scada workstation for logging and displaying time stamped alarms.

The new equipment was designed to fit into the space previously occupied by the original system and was provided pre-wired and tested on back plates. Most of the work was done off-site to save installation time. Furthermore, spare capacity for future expansion was included.

The upgrade provided a modern distributed alarm system with the added benefit of time stamped alarms available to the engineers, if detailed alarm analysis is required.

For more information contact Ian Loudon, Omniflex, +27 31 207 7466,,


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